In many electronic systems today, a boost converter is commonly used to convert a low input voltage to a higher output voltage. The boost converter is particularly useful in low power mobile applications and/or Internet-of-Things (IoT) applications, for example, charging circuit in Bluetooth headphone. There are many applications where the input voltage has a wide range and could either be lower or higher than the output voltage. A single boost converter is not able to cover the entire voltage range in those scenarios.
Conventionally, several types of converters are developed to address the above problem. One such design is to use a non-inverting buck-boost converter to cover the entire range. FIG. 1 shows an example of a conventional non-inverting buck-boost converter. The buck-boost converter 100 includes a first p-type switch P1 110, a first n-type switch N1 120, an inductor L 130, a second n-type switch N2 140, a second p-type switch P2 150, and an output capacitor Cout 160. A source of P1 110 is coupled to an input voltage supply Vdd, and a drain of P1 is coupled to a first terminal of L 130 and a drain of N1 120. A source of N1 120 is coupled to ground. A second terminal of L 130 is coupled to a source of P2 150 and a drain of N2 140. A source of N2 140 is coupled to ground. A drain of P2 150 is coupled to one end of Cout 160. The other end of Cout 160 is coupled to ground.
The buck-boost converter 100 can be configured as either a buck down converter or a boost up converter to convert the input voltage Vdd. However, a complex control scheme is needed to control the four switches, namely, P1 110, P2 150, N1 120, and N2 140, to configure the converter 100 as a buck converter or a boost converter or a buck-boost converter. The four switches needed for power delivery also impose penalties on silicon area and efficiency. Further, the number of pins required in such design is one more than the number of pins required in a conventional regular boost converter.
Another prior design uses a boost converter and a low drop out converter (LDO) in series. FIG. 2 shows a conventional converter 200 having a boost converter and a LDO coupled in series. The converter 200 includes an inductor 210, a first n-type switch N1 220, a first p-type switch P1 230, a boost capacitor C_bst 240, a second p-type switch P2 260, a driver 250, and a LDO capacitor C_ldo 270. Specifically, the inductor 210, N1 220, P1 230, C_bst 240 can be configured as a boost converter 202; while P2 260, driver 250, and C_ldo 270 can be configured as a LDO 204. An input voltage Vin is applied to the inductor 210 and an output voltage Vout is taken at the drain of P2 160.
When input voltage Vin is less than output voltage Vout, boost converter 202 becomes active and boosts up the input voltage Vin. Then LDO 204 down converts the voltage or goes into bypass mode. When Vin is greater than Vout, boost converter 202 goes into bypass mode, and LDO 204 down converts the input voltage Vin.
As shown in FIG. 2, converter 200 needs three (3) switches for power delivery, namely, P1 230, N1 220, and P2 260. Like converter 100 in FIG. 1, the number of pins converter 200 requires is one more than the number of pins required in a conventional regular boost converter. Moreover, two (2) capacitors (i.e., C_bst 240 and C_ldo 270) are required in converter 200, that is one more than the converter 100 shown in FIG. 1. Thus, this design also uses large area on silicon. Further, the arrangement of boost converter 202 and LDO 204 in series imposes an efficiency penalty on the entire design.
FIG. 3 shows a third conventional converter design that uses a boost converter and a LDO in parallel. Converter 300 includes a boost converter 302 having an inductor 310, a n-type switch N1 320, a p-type switch 330, and an output capacitor C_out 360. Converter 300 further includes a LDO 304 having a p-type switch P2 340 and a driver 350. When input voltage Vin is less than output voltage Vout, boost converter 302 is turned on and LDO 304 is turned off. When input voltage Vin is greater than output voltage Vout, boost converter 302 is turned off and LDO 304 is turned on.
Like converter 200 in FIG. 2, converter 300 uses three (3) switches for power delivery, namely, N1 320, P1 330, and P2 340. Thus, converter 300 still requires a large area on silicon. Further, both P1 330 and P2 340 need to have bi-directional block capability due to the parallel configuration.
Because of the various shortfalls of the existing converters discussed above, there is a need in the art to provide a more efficient hybrid boost and LDO converter design that occupies smaller area, especially for the mobile and IoT applications that demand compact design.